#include <cmath>

double f(double x) {
	return sqrt(1.0 - x * x);
}

double calculate_range(double start, double end, double ddx) {
	double x, sum = 0.0;
	for (x = start; x < end; x += ddx) {
		sum += f(x);
	}
	sum = sum * ddx;
	return sum;
}